1. Field of the Invention
The invention relates to the field of volumetric liquid meters and, particularly, to the field of volumetric water meters implementing a technique that is well known to those skilled in the art and is acknowledged for its precision and reliability, namely the technique of the oscillating piston.
2. Description of the Prior Art
Oscillating piston type volumetric water meters have a measuring device formed by a chamber enclosing a piston that is held movably on a flat bottom along a radial partition wall, and between a cylindrical internal wall of said chamber and an external wall of a small guiding cylinder forming a well positioned at the center of its bottom.
The principle of operation of these meters is illustrated schematically in FIGS. 1a to 1d which separate the different steps of the motion of the piston 3 in the chamber 2. During the metering operation, the water enters the device 1 by an intake aperture 13 placed on one side of the radial partition 12. This water fills the two intake housings located before the intake aperture 13, filling them to the maximum extent. A first housing is formed by the space between the external cylindrical wall of the piston 3 and the internal cylindrical wall of the chamber 2 and a second housing is formed by the space between the external cylindrical wall of the well 7 and the internal cylindrical wall of the piston 3. The water to be metered then conveys its energy to the piston 3 which slides along the bottom of the chamber 2 and oscillates in a movement that is characteristic of the technique of the oscillating piston. According to this technique, the axis of the cylinder forming the piston 3 describes a circle about the axis of the cylinder forming the chamber 2. A given volume of water is thus conveyed into two outflow housings towards an outflow aperture 14 positioned on the other side of the partition 12. These housings are located before said outflow aperture 14, one of them being formed by the space between the external wall of the piston 3 and the internal chamber wall of the chamber 2 and the other by the space between the external wall of the well 7 and the internal wall of the piston 3. There is thus a three-stage motion: intake, translation of a volume of water and outflow. This motion occurs in three dual stages since it is done simultaneously with a phase shift equal to PII inside and outside the piston 3.
The water flowing in the conduits conveys solid particles in suspension. These particles come sometimes from the calcareous furring that forms with time in the conduits themselves and that gets detached from time to time, being carried by the flowing water. At other times, these particles come from iron oxide deposits formed in the metal conduits. Furthermore, the water to be metered often conveys yet other particles such as sand particles or more generally siliceous matter.
During a tapping operation, namely when a subscriber to the water service opens a tap to take a quantity of water that he or she needs at a given time, the suspended particles in the water get introduced into the metering device. Here, they are driven rotationally by the piston and follow the path of the water in varying degrees up to the outlet aperture. When the tapping is over, the piston comes to a standstill and the particles that are still suspended in the water contained in the measuring device gradually get deposited slowly at the bottom of the chamber for they generally have a specific gravity greater than that of water. They then form a concentrated deposit referenced 30 in FIG. 2a.
During the next tapping operation, this concentrated deposit is pushed back by the rotating piston 3. It then migrates naturally to the bottom of the device, partly against the internal wall of the chamber 2 and partly against the external wall of the well 7. Here, the particles collect and are piled up, thus forming a wedge 31 shown in FIG. 2b which is carried incessantly by the piston 3 in the feed direction of this piston.
The particles, and especially the particles of siliceous matter which are highly abrasive, scratch and permanently damage the internal side walls of the chamber, the internal and external walls of the piston and the external walls of the well. The friction between the different elements of the device is then more intense and the clearance between the piston and the chamber are accentuated. This increases the leakage of water between the housings. The precision and reliability of the measuring device are thus diminished.
Furthermore, the accumulation of the particles 31 hampers the rotation of the piston 3 and distorts the metering, especially when the piston oscillates at a low rate and then becomes highly sensitive to the forces countering its rotation. The wrong results then obtained are often beyond the permissible limits defined by the legislation in force in most countries.
Furthermore, the wedge 31 may stop the rotation of the piston 3 and block it. In this case, it will be necessary to wait for a tapping at high flow rate so that the water introduced at high pressure create a degree of turbulence in the device that is sufficient to disperse this wedge 31. The solid particles are then again suspended in the water by the piston which resumes its travel. However, they remain to a great extent trapped in the device. It is only with time and provided that the water introduced into the chamber is totally clear, namely totally free of particles, that all the particles will be eliminated. If not, the blocking will probably recur at a later date.
The present invention is aimed at proposing a measuring device that overcomes the above-mentioned drawbacks at lower cost and makes it possible notably to prevent, firstly, the deterioration of said device by the solid particles introduced by the liquid to be metered and secondly the hampering and locking of the piston, and at the same time provides for efficient metrological or industrial measuring performance characteristics even under light operating conditions.
This aim as well as others that shall appear hereinafter are achieved by the presence, in the device, of a groove for the recovery of the particles.